Conventionally, lamps used in automobiles have been connected to lamp sockets. Examples of lamp sockets are disclosed in Japanese Utility Model Application No. 62-64985 and Japanese Utility Model Application No. 62-64986. Such lamp sockets are electrically connected to lamp electrodes at rear ends of the lamps. Other prior art lamp sockets are disclosed in U.S. Pat. Nos. 3,982,813; 4,101,187; DE-A-4139905 and EP-A-0822626.
In recent years, high-illumination discharge (HID) lamps have been used as head lamps in automobiles. Discharge lamps are lamps in which mercury, a metal halide compound or a rare gas, such as xenon, is sealed inside the lamp. In such lamps, light is emitted by causing this substance to discharge by means of a pair of electrodes, thus realizing a high-brightness illumination with the color of sunlight. An important point in light systems using HID lamps is that a high voltage of approximately 20,000 V is required at the time that the discharge is initiated. Accordingly, a shielded cable is used as the cable connected to the lamp socket in order to prevent the generation of electromagnetic interference in other electrical circuits.
Furthermore, in the case of discharge lamps, it is necessary that the connection of the lamp be easily accomplished, and that the lamp have a high degree of safety. Generally, a discharge may occur in the air layer between terminals or conductors to which a high voltage is applied, so that there is a danger that this may be a cause of fire in parts such as connectors, etc. Accordingly, it is desirable that the terminals or conductors of the lamp socket described above be installed so that such a discharge is reliably prevented.